- I added a file into /usr/local/twonky/cgi-bin called ffmpeg.location which just has the text '/opt/bin'
- I added the ffmpeg-all-wav.desc into the same cgi-bin folder
- I added the MimeTypeMapping after all the other MimeTypeMappings in the XBOX_360.xml
- I restarted twonky (restarted the box actually)

Thusfar, I have not seen any difference trying to play music. All of my files (ALAC and AAC) have the m4a extension. AAC files play fine.

Also, I tried the mime type mapping of 'audio/mp4a-latm' instead of 'audio/m4a-latm' since I thought that may have been a typo. I also tested ffmpeg from the command line to convert a ALAC .m4a file to .wav